Complex volatile organic compounds (VOC) are formed during the production of pig iron in the smelting unit on account of the gasification of coal and of further charge materials. Even at high process temperatures, as arise for example in the dome of a smelting unit for producing pig iron, these compounds cannot be decomposed completely or cannot be decomposed in all operating states.
The operation of a smelting unit may form compounds, for example benzene-toluene-xylene (BTX), carbon monoxide, polycyclic aromatic hydrocarbons (PAH) but also cyanides (CN−), which have highly toxic properties. Together with the reducing gas, these compounds pass into the gas cleaning devices, in which case these compounds accumulate, for example, in the water from wet cleaning. Furthermore, these compounds are found in all process gases, for example in the top gas which is removed from the reduction unit. If the contaminated liquid from the wet cleaning, known as process water, is fed into a cooling tower, the evaporation of the process water and of the VOC present therein in the cooling tower may result in considerable environmental pollution.